Biosensors, based on redox enzymes, that provide an amperometric response to the enzyme specific analytes, have been proposed for the determination of analytes such as glucose, lactic acid or choline (A. Heller, Acc. Chenz. Res., 23, 128 (1990) and J. Phys. Chem., 96, 3579 (1992)). Another kind of assay making use of electrodes coated by redox enzymes useful for the detection of the presence and optionally concentration of an analyte in a medium has been described by I. Willner et al. (J. Amer. Chem. Soc., 114, 10965-10966 (1992)). This publication describes the construction of an enzyme immobilized layer on an electrode and the electrical communication between the redox enzyme with the electrode surface by means of a diffusional electron mediator or a protein-linked electron mediator.
The use of electrochemical immunoassays involving electroactive enzyme complexes as signal amplification components has been described by G. A. Robinson et al., J. Immunoassay, 1-15 (1986) and in European Patent Application No. 85303367.8 (Publication No. EP 167248). This immunoassay, which involves the probing of enzyme complexes, has a major drawback in that the activity diminishes with time as well as upon the addition of ingredients which are required for the enzymatic reactions.
The use of a homogeneous electrochemical immunoassay is disclosed in U.S. Pat. No. 5,198,367. This assay involves the preparation of an antigenic redox active protein complex, wherein the electrical communication of the complex with the electrode in the presence of the respective antibody is controlled by the analyte in the solution. The preparation of the three component antigenic-redox relay protein complex is difficult. Furthermore, all electrochemical immunoassays are single-cycle sensing devices and cannot be reused: after a single measurement the activity of the probing complexes is terminated.
Electrobiochemical sensors for the detection of redox inactive biomolecules and particularly biomolecules appearing in sub-micromolar and nanomolar concentration ranges, have important potential applications in diagnostics, food analysis and environmental analysis. Examples can range from detecting antibodies and antigens to tracing undesirable metabolites and herbicides to identifying the presence of toxins and viruses.
It is an object of the present invention to provide an electro-biochemical system for the determination of the presence and optionally the concentration of an analyte in a liquid medium, the analyte being a member of a recognition pair.
It is further an object in accordance with an embodiment of the present invention to provide an electrobiochemical system as above which is substantially reversible and reusable.
It is furthermore the object of the present invention to provide electrodes for use in the above systems.
It is still a further object of the present invention to provide a process for the preparation of such electrodes.